This invention relates to a curable aqueous composition, a method for forming a treated flexible substrate using the curable aqueous composition, and the substrate so treated.
Flexible substrates such as paper, woven fabrics and non-woven fabrics are frequently consolidated or strengthened by treating with a polymeric binder to dispose in or on the substrate. The tensile strength of treated substrate in the status of dry, water immersed (wet) and isopropyl alcohol immersed (IPA) is one of the most important properties to reflect the quality of binder. When a binder treated substrate has high dry, wet and IPA tensile strength, it usually has improved properties including resiliency, crack resistance, dryclean resistance, wash durability, tear strength and fold endurance.
In many instances, the binder is present in a substantially thermoplastic, or substantially uncrosslinked state so that flow, penetration, film formation and the like may occur after the binder solution or dispersion has contacted the substrate. In order to enhance the properties of the treated substrate, it is frequently desirable to effect crosslinking once the binder has achieved its final location, or concurrently with the drying process. Many of the conventional crosslinking agents such as, for example, copolymerized N-methylol acrylamide and added urea/formaldehyde resins inherently contain or liberate formaldehyde.
US patent application 2009/0162669 discloses an aqueous dispersion comprising a polymer and a crosslinker, wherein the polymer is a cyclic anhydride-functional polymer and the crosslinker is a multifunctional hydrazine derivative. This composition is curable at 100° C. for 30 minutes, giving a transparent, colorless film with good chemical resistance to acetone. To obtain such anhydride containing aqueous dispersion, an organic solvent (such as acetone) have to be used to disperse the anhydride containing copolymer in water. Besides, the anhydride containing copolymer is usually obtained from water-free polymerization process. An organic solvent free, environment-friendly pathway is still desired.
U.S. Pat. No. 5,385,756 discloses a method for treating a flexible, porous substrate with a water-borne formaldehyde-free composition which comprises a binder comprising copolymerized dicarboxylic acid monomers or their derivatives. The method provides desired benefits while maintaining substantially formaldehyde-free compositions and processes employing them. However, a fixed base is required prior to treating the porous substrate to partially neutralize with the composition. In order to simplify the application, a one package binder system with efficiently self-curing property is desired.
The problem addressed by this invention is to overcome above defects in the art by providing a curable aqueous composition prepared by an organic solvent free pathway for the treating of flexible or nonwoven substrates with improved processability and acceptable performance.